Acute Bee Paralysis Virus (ABPV) – Symptoms and Diagnosis

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Over the last decade, beekeepers have had to find ways of retaliating against some of the problems they face. These include diseases, pests, parasites, predators, and weather elements. The common diseases that affect honey bees have forced researchers to go back to the drawing board and find ways of countering them. The Acute Bee Paralysis Virus (ABPV), is among the diseases that pose a serious risk to beekeeping enterprises globally. It was discovered for the first time during the laboratory works on the identification of the causative agent of bee paralysis, i.e. the Chronic Bee Paralysis Virus (CBPV).

Just like most other honey bee diseases, the Acute Bee Paralysis Virus can easily be transmitted from one bee colony to the other and across different hives. Bees are social insects that interact while foraging, making it almost impossible to completely eradicate most of the diseases that affect them. Humans also participate in the spread of the diseases through their various activities such as: hive inspection, movement of bees during pollination services, importation of honey bees, and other unhygienic practices.

Differences between the Acute and Chronic Bee Paralysis Viruses

The Acute Bee Paralysis Virus has similar symptoms like those of CBPV. Nonetheless, acute is a term used to denote the increased mortality rate that occurs in bees unlike in the case of CBPV. Another point to note is the fact that virulence in ABPV has a close link to Varroa mite invasion. ABPV is usually passed from the larval jelly by mature bees that are asymptomatic. This is transmitted to the developing larva. It can also be transmitted by the Varroa mites to the bee larvae and pupae. The Acute Bee Paralysis Virus results in early deaths in the infected bees when compared to honey bees with the chronic bee paralysis virus.

Other notable difference between ABPV and CBPV include:

  • ABPV causes infections without obvious symptoms.
  • The spread rate of ABPV greater when there is a longer Varroa feeding period.
  • Any pupa that is infected with ABPV will die before they emerge from the brood cells. It is therefore never easy to notice ABPV. The ultimate effect of this is the dwindling of the honey bee colony and may lead to colony collapse.
  • With ABPV, honey bee colonies can be wiped out within a single season, unlike CBPV.

Prevalence of the Acute Bee Paralysis Virus

ABPV is present in most parts of the world. Countries such as the United States of America, Africa, Asia, Europe, and the Middle East have reported cases of ABPV. The virus belongs to the Dicistroviridae family. The virus is so common and is spread widely in bee colonies, that it has become almost impossible to completely eliminate it.

Acute Bee Paralysis Virus and the Varroa Destructor

The Varroa destructor is the main transmitter of the Acute Bee Paralysis Virus, and the virus has been identified as a cause of colony loss in most honey bee colonies, and mostly whenever there is an infestation of the Varroa destructor. Infected adult bees spread ABPV through the salivary gland secretion as they feed the young larvae. It can also be mixed in the pollen, leading to infection of the young bees. Any infected larvae that ingest a large amount of the virus will die before the brood cells are sealed. Those that survive may emerge as un-infected adult bees.

The Acute Bee Paralysis Virus can remain within the cells in the bees’ body. It can be activated if honey bees are parasitized by Varroa virus or released from the cells. Once activated, it spreads all through the bees system. This may kill the adult bee and can also be transmitted to the brood. In most cases, any affected larvae will die in the cells even before the cells are capped. So far, there is no specific treatment or control measure for ABPV. However, the honey bee colony should be kept free of other diseases and that aggravate ABPV, especially Varroa mites.

The Acute Bee Paralysis Virus is common and it infects most honey bee colonies including healthy ones. However, colony collapse – a common occurrence in honeybee colonies – has been identified as a correlation whenever there is ABPV, coupled with infestation of the Varroa destructor parasitic mite. These mites plays a key role in the spread of various viruses in honeybee colonies, and can worsen the spread of infections.

The Varroa mite is possibly a vector for the ABPV virus. The mite weakens the honey bees substantially and worsens the viral infection, resulting in clinical symptoms and eventual losses in the colonies. Various studies done in the United Kingdom showed that the Acute Bee Paralysis Virus mainly caused a large decline and death in many honey bee colonies, especially in colonies with varroa mite infestation.

Varroa mites cause major infections in honey bees, most of which cannot be easily detected. Some of these infections are sparked and aggravated by favorable environmental factors. In addition to mite and bacterial infections, pollution and overuse of chemicals and insecticides in agricultural enterprises lead to environmental stress in honey bees. There are specific scenarios where the acaricides applied against Varroa mites negatively affect the bee’s immune system, making the bees more susceptible to other infections. The remarkable decline in natural pollinator population as a result of environmental pollution, means the focus has shifted to the use honeybees for pollination of crops and plants. The bees serve an important role both the natural ecosystem and in agriculture. Therefore, healthy bees are important, even far beyond honey production.

Symptoms of the Acute Bee Paralysis Virus

Bees infected with the Acute Bee Paralysis Virus portray a range of symptoms, ranging from no obvious symptom to sudden death, mostly within a few hours.

  • First off, the infected bee will have bloated abdomen caused by a fluid-filled honey sac.
  • Weak trembling wings are another sign of the virus. The infected honey bees crawl on the ground and gather at the hive entrance, due to the weakened wings that render the bees weak and unable to fly.
  • Other notable symptoms in infected honey bees include: the loss of hair in the abdominal area and black and greasy appearance in bees. Once the flying is impacted, the bees lose their strength and eventually succumb to the virus.

In certain cases, honey bees are asymptomatic, showing no symptoms of the disease. You will not be able to identify any of the mentioned symptoms of the disease prior to death. The effect of this is immense, since the infected can transmit the virus outside their own hive.

The presence of dead sealed and unsealed brood was also noted during similar tests for the Acute Bee Paralysis Virus. This therefore made the diagnosis by symptoms difficult to the researchers. The notable nonexistence of bacteria also made it difficult to decipher the virus. Others tests done in Germany and Netherlands showed a strong correlation between ABPV and the degree of varroa mite infestation. Likewise, during peak incidence of ABPV, especially late summer, there was sharp decrease in the adult bee population.

There were also other tests carried out on uninfected bee colonies in Britain. Results showed no ABPV infections in the dead bee samples. This therefore was taken to imply that ABPV is the cause of the high mortality in infested colonies within countries in Europe and beyond. This means, ABPV further worsens the situation in case there is varroa mite infestation.

Other laboratory experiments done have shown that the adult female varroa destructor is a transmitter of ABPV to the healthy honey bee pupae. Tests also showed mites are able to transmit the ABPV 36 hours after they have been taken from an infected host. Additionally, these mites were able to pass on the virus to other hosts.

There is no evidence that can prove viral multiplication in the varroa mite. However, effective transmission of the ABPV occurs. This can be attributed to the fact that the virus is ingested alongside the haemolymph of the infected honey bees. This builds up in the alimentary tract of the mites. Infection can therefore occur due to regurgitation of the gut content when feeding. This is a common occurrence with some plant viruses conveyed by beetles.

At most, 100 particles of the Acute Bee Paralysis Virus is needed to cause infection through injection to the honey bees haemolymph. And laboratory tests showed almost a million times this number of virus in the individual female mites that were collected from naturally infected bee colonies.

The Acute Bee Paralysis Virus can travel harmlessly within the digestive system of the varroa mite. Nonetheless, a small amount introduced to the haemolymph of other host bees or pupae while feeding will infect new hosts. V. destructor and other viral pathogens when in large populations can aid the ABPV leading to colony collapse.

The Acute Bee Paralysis Virus is lethal and it is easily acquired and transferred at a higher rate as compared to the loss of infected honey bee hosts. Also worth mentioning is the increased virus load that occurs in the colony due to contact and exchange of food with infected individuals. This could facilitate the introduction of ABPV.

Routes of Transmission

The Acute Bee Paralysis Virus can readily be transmitted within and between honey bee colonies. It can also be transmitted between other bees and insect species within the area. Transmission of the virus can occur from drone to the queen while mating, from the queen to eggs, from nurse honey bees to the bee larvae while feeding, and between worker bees during trophallaxis. Virus transmission can also take place through the environment, especially when honey bees feed on infected food. These include contaminated honey reserves in the beehive or flowers that are contaminated in the field.

Diagnosis of the Acute Bee Paralysis Virus

Laboratory testing is required for diagnosis of the Acute Bee Paralysis Virus. This involves a complex and detailed analysis of the ABPV genome. This widespread virus that has crippled many apiaries globally poses a serious risk to the survival of the honey bee. One of the genes tested is the capsid polyprotein gene. The tests have been carried out in the past in countries such as the United States, Austria, Hungary, and Germany.  The UK has also been at the forefront when it comes to the diagnosis of the ABPV.

Lab tests have yielded positive results in the past. Scientists have pointed out that ABPV does not belong to any virus genus but is rather described or grouped under the picornaviruses family. These refer to viruses that affect insects and are described as cricket paralysis viruses. The ABPV is similar to Kashmir bee virus in terms of antigenic properties and sequence.

Managing Viral Infections

The Acute Bee Paralysis Virus does not have any prescribed or specific treatment. That therefore means the options for dealing with the disease are few. Fortunately, beekeepers can employ various strategies that will help reduce the spread of the virus and reduce contact with some triggers, such as parasites, pesticides, and nutritional deficiencies. Successful control of the virus will depend on a sound understanding of the biology underlying the viral relationship.

Management programs centered on principles of Integrated Pest Management (IPM) can help curb ABPV. These place an emphasis on reduced dependence of toxic pesticides. Other components of IPM include: the development of economic thresholds, reliance on genetic host tolerance, adoption of cultural practices that disrupt the parasite life cycle, social immune systems, and the use of semiochemicals to trap pests or interfere with their mating. IPM is highly effective when it comes to management of ABPV and other related viruses. It can be expected to delay onset of economic thresholds and minimizes the use of toxic pesticides.

Once economic thresholds are attained, acutely toxic pesticides should be used in rotation and within the lawfully prescribed rates. That way the active ingredients will not be in use successively and it will also prevent the pests from developing some resistance to the active ingredient. Some of the outcomes expected from the use of IPM in fighting diseases and pests include: a reduction in the residues of toxic pesticides in honey bee products and the environment, minimal exposure of beekeepers to the harmful toxins in these chemicals, an extended useful life for the number of recommended pesticides, an improvement in the reproductive performance of queen bees and drones, and a rapid growth in the colony population size and productivity.

1. Cultural Solutions

Use bee stocks that have developed some resistance to Varroa mites. Some of these include; Russian, stocks that are Varroa sensitive, and leg-chewer or ankle-biter stocks. Russian and Varroa sensitive stocks have proven to have an ability to restrain viral populations.

2. Reduce Transmission within and Between Colonies

ABPV virus can be easily spread within and between honey bee colonies. It is particularly easily spread when there is a huge density of honey bee colonies. That means smaller colonies are least likely to be more affected when compared to huge colonies.

Some of the ways that can help the beekeeper reduce transmission include the following:

  • The number of honey bee colonies within each of the apiaries should be reduced. The purpose of this is to minimize spread of the ABPV and other viruses that worsen when bee populations are high.
  • Orientation of honey bee colonies in order to minimize drift of infected bees. The colonies should be kept widely spaced from each other. The colonies can also face different directions and with different markings.
  • You should avoid the movement of frames from the honey bee colony showing symptoms of ABPV to a healthy colony.
  • Use an alcoholic disinfectant to clean hive tools or any other equipment and tools upon inspection and once the symptoms of infection are identified.
  • Proper feeding to the honey bees in case you supplement their feeding. The bees should be fed high-quality products. You can check if the forage within an area close to the apiary provides the right quality of forage or not at any given seasons, whether spring, summer, or fall. The bees can even avoid certain areas implying the forage is of low quality. Once confirmed the forage is of low quality, and/or you realize the bees avoid certain areas for a long period of time, it is time to supplement their diet. Nonetheless, it is important to position the apiary near areas with good quality forage. Studies have established that the pollen collected by bees is of better quality and is good in supporting bee health unlike supplements. Alternatively, you can use a pollen trap to collect the pollen from stronger honey bee colonies and keep this in a freezer for later use.

3. Minimize Contact with Pesticides

It is important for Beekeepers register with local authorities so that they can be alerted whenever a pesticide spray has been scheduled for their locality. It is also wise to engage in helpful conversations with local growers. There are various guidelines that can aid when talking about pesticide application with the local growers.

4. Mechanical Solutions

Old Comb Removal

Old combs should be rotated regularly. This will help eliminate viruses and other contaminants that accumulate for ages. Replace a third of the frames for every colony each year. All old combs should be removed and destroyed.

Propolis Deposits

Honey bees should be encouraged to deposit propolis inside the hive. First off, hive equipment with a rough inner surface will encourage the honey bees fill it up with propolis. You can use rough wood when building hive equipment, especially one side. You can also scratch inner surface of the wood material. Secondly, use a cotton duck cloth as the inner cover. This encourages bees to collect and accumulate propolis. Propolis will help boost immune genes in bees and minimize virus levels in colonies.

5. Chemical Solutions

The Acute Bee Paralysis Virus has no chemical solutions available commercially. However, there are various chemicals that can help minimize viral loads. They are naturally-derived substances that might not be available commercially. These include:

Thymol Treatment

0.16 ppm thymol treatment will reduce ABPV levels when the emerging honey bees are treated with thymol and taken back to their colonies. However, thymol treatment does not give consistent results. It thus requires further studies.

Propolis and Fungal Extracts

You can also reduce ABPV levels by using propolis and fungal extracts. You can apply the propolis solution or Fungal extracts to the interior of beehives. These chemical solutions can help inhibit virus spread. Bees seem to understand this since they instinctively use propolis for coating the hive interior. It is also used on hive entrances. Propolis serves many purposes including keeping off larger invaders. It also helps insulate and disinfects honey bees when entering the beehive.

A Final Word

Like most viral diseases, the Acute Bee Paralysis Virus cannot be controlled by medication. Treatment of the underlying problem may bring improvement in viral infections that occur in close association with specific pathogens or syndromes. Appropriate response to the Acute Bee Paralysis Virus causes of bee mortality requires establishment of standardized diagnostic avenues, establishment of regionalized baseline record keeping that can help discern historic trends in disease incidence, and beekeeper education programs to improve accurate diagnoses at the local level. As these viruses pose a potential source of major economic losses to beekeepers, it is important that the factors worsen these losses and potentially contributing to severe bee mortality be eradicated. An effective control strategy can be developed only by establishing a precise diagnosis and by ruling out other causative agents in all cases.

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